Split beam antenna apparatus for developing angularly oriented beams

ABSTRACT

An antenna apparatus to form a pair of angularly oriented radiation lobes at + OR - 45* with respect to the antenna axis and operating in the X-Band includes a slot radiator in a finite ground plane which generates a multiple lobe radiation pattern generally symmetrical of the antenna axis. A simple rectangular plate reflector is mounted in spaced overlying relationship to the slot radiator. The ground plane has a width of approximately one wavelength and the reflector a width of approximately one and a half wavelength which is separated from the ground plane by approximately one wavelength. The reflector eliminates the onaxis radiation lobe and reinforces the + OR - 45* lobes to form the 90* operating lobes. The reflector plate is secured to the ground plane by a pair of narrow, pin side mounts or integrally interconnected solid and tapered side walls. A series of integral ground plane and reflector units are formed by severing of a rectangular extrusion at appropriately longitudinally spaced inclined planes. By employing an extremely thin wall, a clearance hole may be formed in the ground plane and the waveguide radiating slot used as the feed. Alternatively, the ground plane opening is covered with a low loss, low dielectric cube and a thin electrically conductive foil tape is secured over the spacer to define a properly spaced reflector.

United States Patent [191 Korta et al.

[ 1 SPLIT BEAM ANTENNA APPARATUS FOR DEVELOPING ANGULARLY ORIENTED BEAMS[75] Inventors: Lawrence B. Korta, Hales Comers;

Charles E. Seaks, Jr., Greenfield, both of Wis.

[73] Assignee: Johnson Service Co., Milwaukee,

Wis.

22 Filed: Nov. 28, 1973 21 Appl. No.: 419,494

[52] US. Cl. 343/767; 343/781; 343/784 [51] Int. Cl. ..H01Q 19/14 [58]Field of Search 343/767, 784, 786, 781

[56] References Cited UNITED STATES PATENTS 2,414,376 1/1947 Hcim343/772 2,416,698 3/1947 King 343/772 2,455,286 11/1948 Werner 343/7812,684,444 7/1954 Fales 343/789 2,764,756 9/1956 Zaleski 343/7682,825,062 2/1958 Chu et a1. 343/781 3,593,143 7/1971 Nakahara 343/7683,774,223 1 1/1973 Ehrenspeck 343/781 Primary ExaminerEli LiebermanAttorney, Agent, or Firm-Andrus, Sceales, Starke & Sawall [451 Oct. 7,1975 [5 7 ABSTRACT An antenna apparatus to form a pair of angularlyoriented radiation lobes at i 45 with respect to the antenna axis andoperating in the X-Band includes a slot radiator in a finite groundplane which generates a multiple lobe radiation pattern generallysymmetrical of the antenna axis. A simple rectangular plate reflector ismounted in spaced overlying relationship to the slot radiator. Theground plane has a width of approximately one wavelength and thereflector a width of approximately one and a half wavelength which isseparated from the ground plane by approximately one wavelength. Thereflector eliminates the on-axis radiation lobe and reinforces the i 45lobes to form the 90 operating lobes. The reflector plate is secured tothe ground plane by a pair of narrow, pin side mounts or integrallyinterconnected solid and tapered side walls. A series of integral groundplane and reflector units are formed by severing of a rectangularextrusion at appropriately longitudinally spaced inclined planes. Byemploying an extremely thin wall, a clearance hole may be formed in theground plane and the waveguide radiating slot used as the feed.Alternatively, the ground plane opening is covered with a low loss, lowdielectric cube and a thin electrically conductive foil tape is securedover the spacer to define a properly spaced reflector.

17 Claims, 14 Drawing Figures SPLIT BEAM ANTENNA APPARATUS FORDEVELOPING ANGULARLY ORIENTED BEAMS BACKGROUND OF THE INVENTION Thepresent invention relates to a split beam antenna apparatus andparticularly to a field disturbance detection system employing radiatedelectromagnetic energy into an area to be monitored.

Various detection systems have been developed to monitor movement into,or within, a protected area. A particularly satisfactory system respondsto Doppler motion signals arising from intrusion motion within anelectromagnetic field flodding the protected area. Microwavetransmission was originally developed to produce electromagneticradiation beams which scan the horizon to detect airplanes, ships andthe like within a transmitted field by processing of the signal energyreflected from such object within the field. Such systems have alsorecently been designed to provide reliable intrusion detection in morelimited areas within institutional, industrial and similar units. Theelectromagnetic pattern generated will normally consist of either anelliptical pattern producing a relatively long, narrow pattern and rangefor coverage of an elongated area or a more circular pattern producing arelatively broad area coverage. In various practical applications, thearea to be monitored or protected may not be a continuous area which canbe directly covered by one such pattern. For example L shaped areas suchas the intersecting corridors in a building, perimeter protection oflarge open areas or the like are encountered in intrusion monitoringapplications. Such L shaped patterns can, of course, be readilydeveloped by employing completely separate sources and essentially twocomplete separate systems. The use of two complete units, however, is arelatively expensive construction particularly where relativelysophisticated signal processing is desired to distinguish betweentransient or non-alarm intrusion as compared to actual alarm intrusionconditions. One possible alternative to reducing the expense of such asystem is to employ a pair of power sources with a signal processingcircuit, such, for example, as disclosed in the application of Carl F.Klein et al, now US. Pat. No. 3,859,656, issued Jan. 7, 1 975 andassigned to the same assignee as this application.

Alternatively, a pair of directional atennas can be coupled to a singlemicrowave oscillator through a power divider with each antenna radiatingpower equal to one-half of the peak or total output of the source. Thisreduces the detection range by the familiar radar range equation suchthat the range will be effectively 0.84 of the single beam range. Suchis acceptable where the microwave oscillator cost is a significantportion of the total system cost. Such a system, however, remainsrelatively expensive with present day technology employing the powersplitter and separate antennas. A similar concept can also be employedin L shaped areas if the walls or other confining surfaces are highlyreflective to microwave energy. In such applications, a pattern from theinner corner is directed to an opposed inside corner of the twointersecting corridors with a division of the transmitted energy by thereflecting walls and with the corridors, in effect, acting aswaveguides. Although theoretically possible, such a system is, ofcourse, highly dependent upon the reflective characteristics of thewalls and produces, in effect,

a limitation on the building materials which can be employed.

If a highly reflective characteristic is not encountered, of course, theenergy not reflected is lost, which may result in a significant decreasein the detection range. Further, the system is, of course, highlysensitive to the feed orientation and in-feed pattern of the source.Thus, if it is not very accurately located, a range imbalance willreadily arise which might be, at best, troublesome and, in manyinstances, completely unacceptable.

Thus, although various prior art systems have been suggested, they haveall included significant practical problems for consideration of cost,if not from technical capability, and a significant need for a simple,inexpensive beam splitter exists in the art.

SUNMARY OF THE PRESENT INVENTION The present invention is particularlydirected to a relatively simple and relatively inexpensive split beamantenna apparatus for generating of microwave energy patterns which areangularly oriented with respect to each other, and particularly to suchan antenna apparatus which can generate major radiation lobes at 1 45with respect to the antenna axis and thereby generate a pair of lobesspaced by essentially Generally, in accordance with the presentinvention, a basic electromagnetic pattern is generated by a slotradiator in afinite ground plane which generates a multiple loberadiation pattern generally symmetrical of the antenna axis. Selectionof a suitable ground plane for the slot radiator generates majorradiation lobe ati45 with respect to the antenna axis. Applicants havediscovered that the proper placement of a simple reflector means inoverlying relationship to the slot radiator results in proper reflectionto remove intermediate lobes and, in fact, reinforce the principalangularly related lobes. The reflector means is thus secured to theground plane in spaced overlying relationship to the radiating slot withthe relative size and spacing of the ground plane and reflector selectedto produce the desired pair of concentrated major pattern radiationlobes which may be appropriately spaced generally at 90. The properlyrelated reflector effectively eliminates all other radiation lobes andproduces the reinforcement along thei45 lobe axis. The dimentions of theground plane, the reflector and the separation therebetween produceinterrelated influences with a resultant optimum antenna performance forany given operating frequency. Generally, for a highly satisfactory beamsplitter operating in the standard X-band range and including arectangular ground plane of a width of approximately three wavelengths.Applicants have found a reflector should be of a width of approximatelyone and a half wavelength which is separated from the ground plane byapproximately one wavelength and placed symmetrically over the slot.Generally, with this highly satisfactory operating construction, thepattern was found to be sensitive to a deviation of one-eighthwavelength. The reflector spacing is not particularly significant withrespect to the principal angle of the two lobes, thus indicating thatthe ground plane functions as the primary radiator. The reflectorspacing, however, significantly influences the on-axis radiation and adetectable increase was noted as the reflector is spaced more or lessthan the optimum one wavelength.

The reflector is mounted by suitable supporting spacers secured to theground plane. The spacers are preferably small and/or are removed fromthe aperture in order to minimize the effect on the primary radiationpattern existing in the electric or E-plane, and the magnetic orI-I-plane radiation. The spacers should also be less than a quarterwavelength in width and removed from the aperture if minimum effect onthe pattern is desired. With proper construction the reflector mount ingmeans have an insignificant effect on the E plane pattern and only avery slight effect on the 1-] plane pattern.

More particularly, in a preferred construction, the ground plane patternwas a square metal plate secured to the transmitting end of an X-bandwavelength. A reflector plate was secured to the ground plane by a pairof side members located to the opposite sides of the waveguide openingand in spaced relation to the sides.

In a highly practical beam splitter construction method, in accordancewith the present invention, a rectangular extrusion is provided withopposite walls spaced to define the ground plane and the reflectorintegrally interconnected by side walls. The side walls are tapered,solid metal walls. A series of units are formed by merely severing ofthe rectangular extrusion at appropriately longitudinally spacedinclined planes which are alternately, oppositely inclined such that theground and reflector planes are alternately in the opposite walls of theextrusion and minimize waste material. The integral side walls providesome slight improvement in the radiation pattern, particularly in the Hplane, but the primary advantage in the system resides in the simplifiedfabrication technique. Further, by employing a relatively thin wall, forexample, of the order of 0.025 inches, the edge effects are minimized. Aclearance hole can then be formed in the ground plane with the unitattached to the waveguide, with the actual waveguide radiating slot asthe feed. This results in an extremely simple antenna construction whichcan be produced at minimal cost and properly assembled with thewaveguide.

Further, with this configuration the antenna can be readily adapted to asingle 45 pattern with appropriate direction. For example, if a suitablecover, such as copper tape, is placed over the one aperture, defined bythe tubular formed antenna, energy will be directed from the otheraperture with a slight rotation toward the antenna axis. The pattern canbe rotated by 90 by merely moving the cover, or by otherwise rotating ofthe entire unit.

In a further novel construction, the ground plane is covered with asuitable dielectric spacer with a thin conductive foil disposed,appropriately, over the spacer to secure the spacer in place and definea properly spaced reflector. This produces a relatively narrow reflectorwith a solid plane spacing element spaced quite close to the aperturedwall openings or edges of the aperture.

Thus the present invention employs a conventional ground plane slotradiator in combination with a relatively simply mounted spacedreflector to produce the desired concentrated angularly orientedradiation patterns and thereby provides a relatively simple andinexpensive beam forming system for a microwave intrusion detecting ormonitoring apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings furnished herewithillustrate preferred constructions of the present invention in which theabove advantages and features are clearly disclosed as well as otherswhich will be readily understood from the following description of suchillustrated embodiments.

In the drawings:

FIG. 1 is a diagrammatic illustration of the application of the presentinvention applied to protection of a generally L shaped area defined bya pair of intersecting corridorlike areas;

FIG. 2 is a pictorial view of a split bean antenna unit showndiagrammatically in FIG. 1 and constructed in accordance with thepresent invention;

FIG. 3 is a front elevational view of the split beam antenna apparatusshown in FIGS. 1 and 2;

FIG. 4 is a side view of the apparatus shown in FIGS. 1 and 3;

FIG. 5 is a polar diagram illustrating the normalized radiation patternof the beam splitter antenna apparatus shown in FIGS. 1 4;

FIG. 6 is a view similar to FIG. 5 illustrating the motion detectionpattern of the present invention in relationship to a single pyramidalhorn antenna;

FIG. 7 is a side view of an alternate integrated beam splitter reflectorconstructed in accordance with the present invention with parts brokenaway and sectioned to more clearly illustrate the details ofconstruction.

FIG. 8 is a top view of the antenna apparatus shown in FIG. 7;

FIG. 9 is a bottom view of the apparatus shown in FIG. 7;

FIG. 10 is an end view of the apparatus shown in FIGS. 7 9, inclusive;

FIG. 11 is a pictorial view illustrating a fabrication technique forforming of the beam splitter antenna structures such as shown in FIGS. 710;

FIG. 12 is a diagrammatic illustration showing the application of thestructure of FIGS. 7 10 to generate a downwardly directed pattern;

FIG. 13 is a pictorial view of still a further embodiment of the presentinvention; and

FIG. 14 is an elevational view of the apparatus shown in FIG. 13.

DESCRIPTION OF ILLUSTRATED EMBODIMENT Referring to the drawings andparticularly to FIG. 1, the present invention is illustrated applied tothe protecting of a pair of intersecting elongated areas 1 and 2defining a generally L-shaped configuration. Generally, areas 1 and 2may be defined by confining wall configurations such as the intersectingcorridors of a building as shown, or may be the corner of a large openarea where it is desired to establish a pair of microwave energy fieldpatterns across the entrance into the area from the comer.

In accordance with the present invention, a single microwave energy unit3 is mounted adjacent to the outside comer of the total area defined bythe intersecting corridors 1 and 2. The unit 3 includes an energy beamsource 4 coupled to a beam splitter antenna apparatus 5 constructed inaccordance with the present invention. The apparatus 5 transmits themicrowave energy as two distinct lobes 6 and 7 into the intersectingareas 1 and 2. In the illustrated embodiment of the invention, a singleantenna apparatus 5 is illustrated which will function to both transmitthe basic lobe patterns in the respective areas 1 and 2 and will alsoact as a receiving antenna in the event of intrusion into one or both ofthe patterns 6 and 7. The source 4 also responds to received signalswhich are Doppler motion signals and by suitable processing produces arelated output. Thus, the present invention, as shown, with the singlecombined transmitter-receiver configuration may, for example, beconstructed as shown in the co-pending application of Bailey et al, nowUS. Pat. No 3,750,165 which issued July 31, 1973 and is assigned to thesame assignee as this application. The invention may be employed, ofcourse, with completely separate transmitter and receiver antennas. Assuch systems are wellknown, no further description thereof is given.

Generally, as more clearly illustrated in FIGS. 2 4, the beam source 4illustrated in FIG. 1 includes a square ground plane 8 secured to theouter end of a rectangular waveguide 9 which is mounted and coupled tothe output of an oscillator 10 operating in the standard X-band. Thewaveguide 9, for a standard X-band cross section, may have, for example,a height of 0.4 inches and a width of 0.9 inches. The ground plane is agenerally square ground plane of a height and width of three wavelengthsor approximately 3 inches and is placed symmeteically about slot 11.Thus, the beam is fed from the radiator slot 11 in the finite groundplane 8. In accordance with the teaching of the present invention, amicrowave energy reflector 12 is mounted in spaced overlying relation tothe slot-ground plane radiator 8 and serves to modify the pattern toform the pair of energy lobes 6 and 7 offset by 90, as illustrated inFIG. 1. The reflector 12 is shown, in FIGS. 2 4, mounted in fixed spacedrelation to the ground plane 8 by a pair of spacer members 13 and 14 andis also placed symmetrically about slot 11.

The reflector 12 and the ground plane 8 are sized, shaped and positionedrelative to each other to essentially remove all but the pair ofradiation lobes 6 and 7 and to particularly generate the desiredradiation pattern at i 45 from the major axis of the slot radiator 11.

Generally, it is known that a slot radiator in a finite ground plane ofthree wavelengths diameter will generate an energy pattern having a mainlobe on the axis of the slot radiator and a pair of side lobes withrespect to the principal axis. Applicants have found that the squareground plane produces a similar pattern configuration with the lobesapproximately i50,,off the major axis lobe. In accordance with thepresent invention, the simplereflector 12.is\locatedto remove theradiated energy from the principal axis and to reinforce the angularlyoffset pattern lobes 6 and 7, as clearly shown in FIG. 5. The reflector12 configuration for optimum operation and separation of the lobes had alength of approximately three wavelengths, and thus equal to the groundplane, and a width of approximately 1% wavelengths.

The actual length of the ground plane does not essentially effect theE-plane radiation pattern as long as the length is approximately atleast equal to 1 /2 wavelength. The reflector spacing does notmaterially affect the angular orientation of the operating lobes 6 and7, indicating that the ground plane structure functions as the primaryenergy radiator. The spacing, however, did appreciably influence theon-axis radiation which tended to increase as the reflector spacing wasvaried to either side of the optimum one wavelength spacement.

Further, as long as the spacing elements were maintained one-quarterwavelength or less in width and removed from the sides of the aperture,no material adverse influence on the patters is detected. Onlyinsignificant influence is found in the primary radiation pattern in theelectric or E-plane and only a slight adverse effeet in the magnetic orl-l-plane.

Generally, Applicants have found that the radiating aperture or slotdimensions are not critical although for optimum operation, the feedpolarization must be maintained. This teaching is particularlysignificant where impedance matching considerations are required. Thus,the slot can be now selected to produce a relatively wide range ofimpedance values without destroying the radiation dividercharacteristic.

A typical, normalized radiation pattern of a beam splitter antennaapparatus, such as shown in FIGS. 1 4, is illustrated in the polardiagram of FIG. 5. As illustrated therein, the energy lobe on the axisof the slot radiator has been completely eliminated with the pair oflobes 6 and 7 generated generally rotated 50 from the principal axis.This clearly illustrates the highly desired approximately 90relationship between the two operating lobes as generated by the beamsplitter antenna apparatus 5 of the present invention.

A similar illustration for the single head motion detector such as shownin FIGS. 1 4 is also shown in FIG. 6. Superimposed on the illustrationof FIG. 6 is an on-axis pattern 15 generated by the use of the sameoscillator source with a single 16 db pyramidal horn antenna structure.The illustration of FIG. 6 indicates that the beam splitter antennaapparatus reduces the detection range in either lobe generally to theorder of that provided by the pyramidal horn. This is in accordance withthe anticipated result based on the radar range equation whichinterrelates detection range to the square root of the antenna gain forany given single antenna system. The beam splitter antenna structure ofthe invention is, therefore, the equivalent of a pair of separate powersources feeding two optimum gain 14 db pyramidal horns. Further, thereflector construction of the present invention minimizes mutualcoupling between the transmitting apertures formed to the opposite sidesof the slot 1 l and thereby increases the sharpness of the resultantnull axis over that obtained with a pair of horns.

The invention, of course, is applicable to any closed or open area asthe beam separation is not dependent upon the existence or sensitivityof any confining portions or wall of the areas 1 and 2. The system ofthis invention which employs the formation of the lobes as a direct partof the energy permits accurate factory construction and mounting of thereflector so as to create an accurate beam splitting. The high degree ofaccuracy which can be readily attained essentially prevents anyundesired range imbalance.

Thus, the present invention provides a simple and inexpensive means ofaccurate formation of a pair of operating energy lobes for portection ofangularly oriented areas.

Other methods of forming the interrelated ground plane and reflectorwith appropriate spacing of the reflector, may, of course, be employed.A particularly practical and simplified production construction isillustrated in FIGS. 7 10, and one which is particularly adapted to amass production process. The structure shown in FIGS. 7 10, inclusive,includes an integral rectangular ground plane 16 and reflector 17connected by a pair of integral solid side walls 18 and 19 instead ofthe spacers l3 and 16 of FIG. 2. The side walls 18 and 19 providetapered side edges 20 extending between the outer edges of the reducedwidth of the reflector 17 and the full width of the ground plane 16. Inthe illustrated construction, the ground plane 16 includes the radiatingslot 21 and a plurality of mounting openings 22 for interconnection ofthe ground plane to a waveguide.

For simplification of the system, the ground plane 16 may be formed witha clearance hole 23, as shown in phantom in FIG. 8, slightly greater indiameter than the width of the radiating slot in the normal slotposition. Applicants have found that if the waveguide and, particularly,the ground plane wall 16 is formed of a relatively thin material, forexample, of the order of 0.025 inches, that the edges of the opening 23will have negligible effect. The unit is mounted on a waveguide as shownin FIG. 1 with a mounting flange, similar to flange 8, provided withopenings corresponding to location of openings 22 and the slot formedthereby is used as the feed means. For example, in the assumed groundplane for an X-band signal, the opening 23 may be of a 1 inch diameterwith the space between the radiator slot and the clearance openingclosed by the mounting flange.

As noted previously, the advantage of this particular beam splitterantenna apparatus is its adaptation to practical production processes.

Thus, as shown in FIG. 11, a rectangular elongated member 24 is formedof a suitable metal for the ground plane and the reflector and a crosssection corresponding to the cross section of the integral ground planeand reflector, for example, as shown in FIG. 10. A series of the beamsplitter antenna apparatus 25 is formed by merely severing of therectangular extrusion along appropriate inclined side edge lines 26.Further, the successive beam splitter units 25 are formed with thereflector and ground planes formed from the walls of the rectangularextrusion to eliminate waste material. The opposite walls of therectangular extrusion 24 are further formed or provided with theproperly spaced mounting openings 22 as well as the necessary radiatingaperture or clearance opening 23.

This construction may, of course, be readily employed in practical, massproduction of the antenna while maintaining the desired accuracy of beamsplitting.

Further, such a unit can, of course, be readily adapted to a single loberadiation pattern which is appropriately directed by the angularorientation of the source and antenna. For example, as shown in FIG. 12,a radiation transceiver 27 having an antenna apparatus 28, such as shownin FIGS. 7 10, is mounted to the side wall 29 of an area to beprotected. The source and associated antenna apparatus are oriented tolocate the transmitting apertures in a vertical plane. The upperaperture is blocked as by a strip of copper tape 30. As a result of thecovering of this aperture and the angular orientation, a singleoperating lobe 31 is provided projecting downwardly toward the floor 32.

If an oppositely directed lobe is desired, the cover 30 can be placed onthe opposite aperture, or the total unit can be rotated Any otherangular orientation can, of course, be provided to appropriately directthe protective lobe.

Other configurations can also be employed and a further embodiment ofthe invention is illustrated in FIGS. 13 and 14. In the illustratedembodiment of the invention, a ground plane member 33 is formed as asuitable plate having the appropriate mounting openings 34 and radiatingslot 35. In accordance with the present invention, a cube 36 of asuitable microwave transmitting material, such as a dielectric foam, ismounted in abutting relation to the exterior face of the ground plane 33and centrally located in overlying relationship to the transmittingaperture 35. A tape 37 of copper or any other suitable energy reflectivematerial is wrapped over the outer periphery of the cube 36 and extendsdownwardly along the sides of the cube to the top and bottom of the slot35. The terminal ends 38 and 39 of the tape 37 are appropriately bentover into abutting relation to the outer face of the flange 33 andsecured thereto as by suitable adhesive 40. The integral side walls 41define the spacers, which in the illustrated embodiment of theinvention, are quite closely spaced with respect to the edges of thetransmitting aperture 35.

The close location of the spacers to the edges does provide a noticeableinfluence on the pattern and produces a change in the effective size ofthe reflector. Generally, Applicants have found that the side walls willreduce the E plane lobes while increasing the H plane radiation. Forexample, employing a one inch cube of low density polystyrene foam(Styrofoam) with a one inch wide copper tape of a 0.0035 inch thicknesssuch as 3M X1 181 copper foil tape generated a highly acceptable splitradiation pattern such as shown in the previous figures. However, thesolid plane spacer walls reduced the gain in the E-plane lobe byapproximately 1 db while providing a corresponding increase in the Hplane radiation, which, for most practical application, is a readilyacceptable pattern configuration. Thus, the embodiment of the inventionillustrated in FIGS. 13 and 14 produces another simple and practicalconstruction adapted to be a relatively simple fabrication techniquewhich is readily within the scope of present technology. Thus, thedielectric foam material is already largely employed in microwavetransmission systerns and can be readily formed into appropriately sizedcubes. Copper tape, of course, is also readily available and can beeasily formed over the dielectric foam cube and appropriately applied tothe metal ground plane member.

The present invention therefor provides a relatively simple andinexpensive beam splitter antenna apparatus which creates the necessarydirectional patterns for microwave motion detectors of offset areas andthe like and which can be constructed in many different practicalproduction methods.

Various modes of carrying out the invention are con- We claim:

1. A beam splitting antenna apparatus for developing selected angularlyrelated operating radiation lobe means comprising a hollow rectangularwaveguide terminating in a slot opening in a finite essentially planarground plane member terminating in outer free space edges, saidwaveguide and ground plane member forming a slot radiator developing aradiation pattern inclusive of the slot axis and to the opposite sidesof the axis with the pattern projecting laterally outwardly of said freespace edge, and a rectangular, planar reflector generally correspondingto the slot opening of the waveguide, mounting means fixedly mountingsaid reflector in outwardly spaced overlying relationship to said groundplane member with the reflector overlying the slot opening and theadjacent ground plane member and spaced from said slot opening and saidground plane to control the radiation pattern on the axis of the slotand thereby the angularly offset radiation lobes.

2. The beam splitting antenna apparatus of claim 1, wherein said groundplane member is formed to gener ate a pair of major radiation operatinglobes generally at i 45 from the antenna axis as well as intermediateradiation lobes therebetween, and said reflector essentially eliminatessaid intermediate radiation lobes and reinforces said operating lobes.

3. The beam splitting antenna apparatus of claim 1, wherein said groundplane member is a square plate having a centrally located slot opening,said ground plane member generates a pair of major radiation operatinglobes generally at i 45 from the antenna axis as well as theintermediate radiation lobes therebetween, and said reflector being arectangular plate spaced from the ground plane member by essentially onewave length and essentially eliminating said intermediate radiationlobes and reinforcing said operating lobes.

4. in the apparatus of claim 1 including a transceiver for generating ofa microwave energy and for detecting reflected microwave energy.

5. The beam splitter antenna apparatus of claim 1 wherein said reflectoris a flat plate spaced from the slot opening by one wavelength.

6. A beam splitting antenna apparatus for developing selected angularlyrelated operating radiation lobe means comprising a finite essentiallyplanar ground plane member terminating at least one outer free spaceedge having a slot for formation of a slot radiator developing aradiation pattern inclusive of the slot axis and to the opposite sidesof the axis and projecting laterally outwardly of said free space edge,and a reflector secured in outwardly spaced overlying relationship tosaid ground plane member with the reflector means overlying the slotopening and the adjacent ground plane member and spaced from said groundplane to control the radiation pattern on the axis of the slot andthereby the angularly offset operating radiation lobes, wherein saidground plane member and said reflector member are integrally connectedby solid side wall metal members spaced from said free space edge.

7. The antenna apparatus of claim 1 including a microwave sourceoperating in the X-Band and connected to said rectangular waveguide.

8. The antenna apparatus of claim 7 wherein said waveguide terminates ina mounting flange and said ground plane member is secured to saidmounting flange, said ground plane member being formed with a clearanceopening aligned with the waveguide slot opening within the mountingflange and said ground plane member is of a sufficiently thin materialsuch that the edges of the clearance hole do not appreciably affeet thepattern generated from the combination of the radiating slot opening andthe ground plane member.

9. The antenna apparatus of claim 7 wherein said ground plane member hasa width of essentially three wavelengths and said reflector has a widthof essentially one and one-half wavelengths.

10. The antenna apparatus of claim 7 wherein said reflector is spacedfrom said ground plane member by essentially one wavelength.

11. The antenna apparatus of claim 8'said clearance opening is locatedconcentrically about said radiating slot opening and of a size to spacethe opening from the edge of the radiating slot opening.

12. The beam splitter apparatus of claim 7 wherein said reflector isspaced from said ground plane member by essentially one wavelength.

13. The beam splitter antenna apparatus of claim 12 wherein said groundplane member has a width of essentially one and one-half wavelengths.

14. The beam splitter antenna apparatus of claim 13 wherein saidreflector eliminates the slot axis radiation lobe and generates saidangularly offset operating radiation lobes offset essentially fiftydegrees from the slot axis.

15. The apparatus of claim 1 wherein said ground plane opening iscovered by a dielectric material defining a microwave energytransmitting medium and with the outer surface thereof spaced inaccordance with the location of said reflector, said reflector beingformed by a tape member of a microwave energy reflective materialsecured to the outer surface of said material and to said ground planemember.

16. The apparatus of claim 15 wherein dielectric material is arectangular cube with one face abutting the back side of the groundplane member and said tape extends across said cube and downwardly alongthe side walls of the side walls of the cube adjacent the sides of theradiating slot opening, and means securing the ends of the tape to theground plane member to mount the reflector and cube in overlyingrelationship to said radiating slot opening.

17. The apparatus of claim 1 wherein said ground plane opening iscovered by a dielectric foam cube defining a microwave energytransmitting medium and with the outer surface thereof spaced inaccordance with the location of said reflector, said reflector beingformed by a tape of a microwave energy reflective material, said tapeextending across said cube and downwardly along the side walls of thecube adjacent the sides of the radiating slot opening, and means tosecure the ends of the tape to the ground plane to mount the reflectorand cube in overlying relationship to said radiating slot opening.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. v: 3 911 44 DATED October 7, 1975 INV ENTOR(S) LAWRENCE B.KORTA ET AL It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, Line 13, after "field" cancel "flodding" and insert floodingcancel "Wavelength" and insert Waveguide Column 3, Line 15,

Column 3, Line 51, after "moving" insert Column 9, Line 32, after "as"cancel "the".

(CLAIM 3) Signed and Scaled this twenty-seventh D f January 1976 [SEAL]Attest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN (ummisxioner ofPatentsand Trademarks

1. A beam splitting antenna apparatus for developing selected angularlyrelated operating radiation lobe means comprising a hollow rectangularwaveguide terminating in a slot opening in a finite essentially planarground plane member terminating in outer free space edges, saidwaveguide and ground plane member forming a slot radiator developing aradiation pattern inclusive of the slot axis and to the opposite sidesof the axis with the pattern projecting laterally outwardly of said freespace edge, and a rectangular, planar reflector generally correspondingto the slot opening of the waveguide, mounting means fixedly mountingsaid reflector in outwardly spaced overlying relationship to said groundplane member with the reflector overlying the slot opening and theadjacent ground plane member and spaced from said slot opening and saidground plane to control the radiation pattern on the axis of the slotand thereby the angularly offset radiation lobes.
 2. The beam splittingantenna apparatus of claim 1, wherein said ground plane member is formedto generate a pair of major radiation operating lobes generally at +or - 45* from the antenna axis as well as intermediate radiation lobestherebetween, and said reflector essentially eliminates saidintermediate radiation lobes and reinforces said operating lobes.
 3. Thebeam splitting antenna apparatus of claim 1, wherein said ground planemember is a square plate having a centrally located slot opening, saidground plane member generates a pair of major radiation operating lobesgenerally at + or - 45* from the antenna axis as well as theintermediate radiation lobes therebetween, and said reflector being arectangular plate spaced from the ground plane member by essentially onewave length and essentially eliminating said intermediate radiationlobes and reinforcing said operating lobes.
 4. In the apparatus of claim1 including a transceiver for generating of a microwave energy and fordetecting reflected microwave energy.
 5. The beam splitter antennaapparatus of claim 1 wherein said reflector is a flat plate spaced fromthe slot opening by one wavelength.
 6. A beam splitting antennaapparatus for developing selected angularly related operating radiationlobe means comprising a finite essentially planar ground plane memberterminating at least one outer free space edge having a slot fOrformation of a slot radiator developing a radiation pattern inclusive ofthe slot axis and to the opposite sides of the axis and projectinglaterally outwardly of said free space edge, and a reflector secured inoutwardly spaced overlying relationship to said ground plane member withthe reflector means overlying the slot opening and the adjacent groundplane member and spaced from said ground plane to control the radiationpattern on the axis of the slot and thereby the angularly offsetoperating radiation lobes, wherein said ground plane member and saidreflector member are integrally connected by solid side wall metalmembers spaced from said free space edge.
 7. The antenna apparatus ofclaim 1 including a microwave source operating in the X-Band andconnected to said rectangular waveguide.
 8. The antenna apparatus ofclaim 7 wherein said waveguide terminates in a mounting flange and saidground plane member is secured to said mounting flange, said groundplane member being formed with a clearance opening aligned with thewaveguide slot opening within the mounting flange and said ground planemember is of a sufficiently thin material such that the edges of theclearance hole do not appreciably affect the pattern generated from thecombination of the radiating slot opening and the ground plane member.9. The antenna apparatus of claim 7 wherein said ground plane member hasa width of essentially three wavelengths and said reflector has a widthof essentially one and one-half wavelengths.
 10. The antenna apparatusof claim 7 wherein said reflector is spaced from said ground planemember by essentially one wavelength.
 11. The antenna apparatus of claim8 said clearance opening is located concentrically about said radiatingslot opening and of a size to space the opening from the edge of theradiating slot opening.
 12. The beam splitter apparatus of claim 7wherein said reflector is spaced from said ground plane member byessentially one wavelength.
 13. The beam splitter antenna apparatus ofclaim 12 wherein said ground plane member has a width of essentially oneand one-half wavelengths.
 14. The beam splitter antenna apparatus ofclaim 13 wherein said reflector eliminates the slot axis radiation lobeand generates said angularly offset operating radiation lobes offsetessentially fifty degrees from the slot axis.
 15. The apparatus of claim1 wherein said ground plane opening is covered by a dielectric materialdefining a microwave energy transmitting medium and with the outersurface thereof spaced in accordance with the location of saidreflector, said reflector being formed by a tape member of a microwaveenergy reflective material secured to the outer surface of said materialand to said ground plane member.
 16. The apparatus of claim 15 whereindielectric material is a rectangular cube with one face abutting theback side of the ground plane member and said tape extends across saidcube and downwardly along the side walls of the side walls of the cubeadjacent the sides of the radiating slot opening, and means securing theends of the tape to the ground plane member to mount the reflector andcube in overlying relationship to said radiating slot opening.
 17. Theapparatus of claim 1 wherein said ground plane opening is covered by adielectric foam cube defining a microwave energy transmitting medium andwith the outer surface thereof spaced in accordance with the location ofsaid reflector, said reflector being formed by a tape of a microwaveenergy reflective material, said tape extending across said cube anddownwardly along the side walls of the cube adjacent the sides of theradiating slot opening, and means to secure the ends of the tape to theground plane to mount the reflector and cube in overlying relationshipto said radiating slot opening.